1. Field of the Invention
The present invention relates to a method for manufacturing a display device and a liquid crystal display device, and more particularly to a technique which is effectively applicable to a method for manufacturing a liquid crystal display device.
2. Description of the Related Art
Conventionally, an active-matrix-type liquid crystal display device has been popularly used as a display for a television receiver set or a personal computer, a display for a portable electronic equipment such as a mobile phone and a portable gaming machine, for example.
The active-matrix-type liquid crystal display device is a display device having a liquid crystal display panel in which a liquid crystal material is sealed in a gap defined between a pair of substrates. A display region of the liquid crystal display panel is constituted of amass of pixels each of which has a TFT element, a pixel electrode, a counter electrode and a liquid crystal layer, for example.
When a liquid crystal display device displays a video or an image on a display screen thereof, in each pixel of the liquid crystal display panel, transmissivity of light emitted from a backlight, reflectance of ambient light, or both of these properties are controlled. Here, transmissivity and reflectance of light in each pixel are controlled based on the alignment direction of a liquid crystal layer (liquid crystal molecules) interposed between a TFT substrate and a counter substrate. The alignment direction of the liquid crystal layer is mainly controlled based on the magnitude of potential difference between a pixel electrode and a common electrode or the direction of an electric field which is applied to the liquid crystal layer when such potential difference is generated. Here, a method for arranging pixel electrodes and common electrodes is roughly classified into a method such as a VA method or a TN method in which the pixel electrodes and the common electrodes are arranged with a liquid crystal layer sandwiched therebetween, and a method such as an IPS method in which the pixel electrodes and the common electrodes are arranged on one of a pair of substrates.
In the IPS method, pixel electrodes and common electrodes are formed on the same plane of an insulation layer, for example. Here, the pixel electrode and the common electrode have a planar comb-like shape, and comb-teeth portions of both electrodes are arranged alternately. Further, in the IPS method, the pixel electrode and the common electrode may be stacked by way of an insulation layer, for example. Here, with respect to the pixel electrode and the common electrode, a planar shape of the electrode arranged closer to a liquid crystal layer is formed into a comb-like shape.
In arranging the pixel electrode and the common electrode on the same plane of the insulation layer, it is usually necessary to form these electrodes such that a gap between the comb-teeth portion of the pixel electrode and the comb-teeth portion of the common electrode in each pixel becomes substantially equal. On the other hand, in stacking the pixel electrode and the common electrode, with respect to the electrode arranged closer to the liquid crystal layer, it is necessary to form the electrode such that a gap between the respective comb-teeth portions become substantially equal.
In a step of forming the pixel electrodes and the common electrodes, these electrodes are generally formed by etching a transparent conductive film such as an ITO film. Here, in a conventional method for manufacturing a liquid crystal display panel, a photosensitive material film formed on the transparent conductive film is exposed by an exposure device which uses a photo mask and, thereafter, unnecessary portions of the transparent conductive film are removed using an etching resist obtained by development as a mask.
However, in manufacturing the liquid crystal display panel, usually, the liquid crystal display panel is manufactured using mother glasses having a large area. Accordingly, when the photosensitive material film is exposed by the exposure device using the photo mask, for example, a pattern of light at a portion of the photosensitive material film corresponding to an edge portion of the photo mask is distorted, so that the irregularity in line width of the pixel electrode and the common electrode is liable to become large.
To cope with such a drawback, in a recent method for manufacturing a liquid crystal display panel, there has been proposed a method which, in exposing a photosensitive material film, uses an exposure device referred to as a multi-beam exposure device instead of an exposure device which uses a photo mask.
The multi-beam exposure device is a kind of exposure device of a type referred to as “direct-writing-exposure type” or “direct-exposure type”, and forms a pattern of light radiated to a photosensitive material film by performing a numerical control of an MEMS such as a DMD instead of using a photo mask. That is, the direct-writing-exposure-type exposure device can change the pattern of light radiated to the photosensitive material film by correcting numerical data used for the control thus easily reducing irregularity in line width of the pixel electrode and the common electrode, for example.